compiler flag for "preview all"

[Bruce Carneal]

On Monday, 29 June 2020 at 23:43:11 UTC, rikki cattermole wrote:
> -preview=d3
>
> dmd3 = dmd2 -preview=d3
>
> Any major breaking changes would not be turned on in D2.
>
> Not a new idea ;)

Well, the scope is a little different.  preview=all would refer 
to currently implemented preview features which are, presumably, 
less controversial than a d3 moniker would imply.  Implementing 
-preview=all could be as simple as replacing a string within 
args[] with a table of strings (which table probably already 
exists).

But yeah, same general idea.  A simpler way for us to test 
against possible futures.